For example, my postgresql-main.log contains entries such as the following:

process 20234 session 5901502e.4f0a vtransaction  transaction 0 : LOG:  connection received: host=[local]
process 20234 session 5901502e.4f0a vtransaction 2/1 transaction 0 : LOG:  connection authorized: user=postgres database=postgres
process 20234 session 5901502e.4f0a vtransaction 2/2 transaction 0 : LOG:  statement: SELECT d.datname as "Name",
           pg_catalog.pg_get_userbyid(d.datdba) as "Owner",
           pg_catalog.pg_encoding_to_char(d.encoding) as "Encoding",
           d.datcollate as "Collate",
           d.datctype as "Ctype",
           pg_catalog.array_to_string(d.datacl, E'\n') AS "Access privileges"
    FROM pg_catalog.pg_database d
    ORDER BY 1;
process 20234 session 5901502e.4f0a vtransaction  transaction 0 : LOG:  disconnection: session time: 0:00:00.004 user=postgres database=postgres host=[local]
process 20237 session 5901502f.4f0d vtransaction  transaction 0 : LOG:  connection received: host=[local]
process 20237 session 5901502f.4f0d vtransaction 2/3 transaction 0 : LOG:  connection authorized: user=postgres database=postgres
2017-04-26 19:58:07 MDT process 20237 remote [local] session 5901502f.4f0d vtransaction 2/4 transaction 0 : LOG:  statement: SELECT d.datname as "Name",
           pg_catalog.pg_get_userbyid(d.datdba) as "Owner",
           pg_catalog.pg_encoding_to_char(d.encoding) as "Encoding",
           d.datcollate as "Collate",
           d.datctype as "Ctype",
           pg_catalog.array_to_string(d.datacl, E'\n') AS "Access privileges"
    FROM pg_catalog.pg_database d
    ORDER BY 1;
process 20237 session 5901502f.4f0d vtransaction  transaction 0 : LOG:  disconnection: session time: 0:00:00.002 user=postgres database=postgres host=[local]

Is there any relation between virtual transaction ids 2/1 and 2/2 above since they share the prefix 2/?